1. Field of the Invention
This invention relates to the provision of novel sequiterpene epoxides and ways of preparing and using the novel compounds.
2. Description of the Art
The stink bug Nezara viridula (Hemiptera: Heteroptera: Pentatomidae) is native to the Ethiopian region, but has been spread by commerce to every continent and many islands between 45.degree. north and south latitudes. Both the adult and immature bugs feed on developing fruits and seeds by sucking sap or oil through hypodermic-like mouthparts. Thus, the insects directly damage the most valuable portion of a crop, yet the damage is not as obvious as for insects eating foliage. Feeding by N. viridula also indirectly reduces yield and seed quality by transmission of diseases.
Nezara attacks a wide range of fruit, field crops, vegetables, and nut crops. In the United States, N. viridula (called the southern green stink bug) is a major pest of soybean south of a line extending from Texas in the west through southern Arkansas to Virginia in the east. The insect (called the green vegetable bug in some other countries) is also a major and frequent pest of soybean in Central and South America, China, Korea, Japan, India, Australia, New Zealand, and Africa. In the U.S., the bug is an unpredictable, occasional pest of pecans and some vegetables, particularly tomatoes. The southern green stink bug has recently extended its range to California where it has already become a pest of tomatoes. In Japan and other rice-producing countries, N. viridula can be a serious pest of this crop.
Nezara adults are strong fliers and frequently migrate to different fields of the same or other maturing crops. In the absence of food or with the onset of winter in warm temperate regions, adults are able to hibernate and resume attack the following season. In many parts of the world where N. viridula is established there is a scarcity of effective parasites and predators despite efforts to introduce these biocontrol agents. Their initially inconspicuous feeding damage, combined with a facility for migration and lack of natural enemies, make N. viridula an especially difficult pest to control.
One control tactic that is somewhat effective in reducing Nezara infestation of soybean is the trap crop technique. This method entails planting small acreages of soybean 10-14 days earlier than the main crop. The early maturing soybean attracts migrating Nezara adults which mate and reproduce in the trap crop. Maturing second generation bugs are then destroyed by insecticide application. This approach is economical because relatively small areas are sprayed, and minimizes environmental pollution and destruction of natural enemies. However, incomplete attraction of adult bugs and the ability of the adults to evade insecticide treatment are serious drawbacks to this control strategy.
A chemical attractant, such as the synthetic sex pheromones available for many kinds of moths, would be a valuable tool for monitoring and manipulating Nezara populations. Field tests using caged bugs have demonstrated that N. viridula adult males release a pheromone attractive to conspecific male and female adults and fifth-instar nymphs, and that Trichopoda pennipes (Diptera: Tachinidae), a fly that is parasitic on N. viridula, uses the pheromone as a kairomone (Mitchell and Mau, Journal of Economic Entomology 64: 856-859 (1971); Harris and Todd, Entomol. Exp. & Appl. 27: 117-126 (1980)). However, attempts to identify the pheromone have met with only limited success. Pavis (These de 3 Cycle de Biologie animale, Universite de Paris-Sud Centre d'Orsay (1986)) and Pavis and Malosse (C. R. Acad. Sc. Paris Series III, 7:273-276 (1986)) reported the presence of two pairs of isomers having molecular weights (MW) of 220 and 224 in two fractions of a hexane extract from the ventral abdominal integument of mature males of European N. virdula. The fraction containing the 224 MW compounds reportedly was attractive to N. viridula females, and the fraction containing the 220 MW compounds reportedly served as a mating stimulant. The four compounds were tentatively characterized as cyclic sesquiterpenes, but the compounds were not individually isolated and the structures were not identified.